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Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.
Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
It is difficult to obtain enough calcium without consuming milk or other dairy foods.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.